>>63950269
Nothing happening in the "dark ages" (retarded name btw) is mostly up to economics, but even so they still went through plenty of development throughout those times, going from late-roman or in some cases barbarian-tier tech to late medieval. The black death in particular did a lot to focus wealth and land into fewer hands.
The mongols wrecked shit when they first came to eastern europe but crashed hard the second time around pretty much just because of the near constant escalation between local powers.